I've found sort of "fix" for this: I hope someone will come with a more elegant way, in meanwhile, for those google's traveler, here's how I am doing it actually:
Make a regular escoria item as said here: https://fr.flossmanuals.net/creating-point-and-click-games-with-escoria/the-items/
And attach the escoria script, with the stuff you want, in the Event Path. ie:
say "this is the escoria script I want to use in the regular GDScript."
Now attach the escoria node as child of the node that use your main GDScript... you can name your "slave" escoria node whatever you want, I do call it just "slave"
Whenver in your main GDSscript run a:
the slave node will perform the escoria escoria script you need (in this example, the player will simply speak). You can also hide the slave node, since we don't really use it.